Screw mechanisms for focusing optical instruments or for other purposes



Sept. 1, 1936. w. TAYLOR 2,053,231

SCREW MECHANISMS FOR FOCUSING OPTICAL INSTRUMENTS OR FOR OTHER PURPOSES Filed Aug. 51, 1935 2 Sheets-Sheet l INVENTOR. 60M 9 A; ATTORNEY.

Sept. 1, 1936. w. TAYLOR 2,053,231

SCREW MECHANISMS FOR FOCUSING OPTICAL INSTRUMENTS OR FOR OTHER PURPOSES Filed Aug. 31, 1935 25heets-Sheet 2 INVENTOR.

jam 4).. (W

A; ATTORNEY.

Patented Sept. 1, 1936 2,053,231

UNITED STATES PATENT OFFICE SCREW MECHANISMS FOB FOCUSING P- TIOAL INSTRUMENTS OR FOR OTHER PURPOSES William Taylor, Leicester, England, aaaignor to Kapdla Limited, Ldeeater, England, a corporation of England Application Angnat 31, 1935, Serial No. 38,719 In Great Britain September 4, 1934 l cum. (CI. 95-45) This invention relates to precisionscrewmechadapted for attachment to a camera and conanisms of the kind comprising a fixed member, taining a balanced key member; a rotatable member mounted for rotation there- Fig. 4 is a front elevation of the same; on, and a slidable member adapted to be moved Fig. 5 is a front elevation of a rotatable mem- 5 longitudinally along the axis of the rotatable ber for the mechanism; 5

member by such rotation. Such mechanism is Fig. 6 is an axial section of the same; needed particularly in optical apparatus as a Fig. 7 is a front elevation of a balanced key; means of focusing and, for example, in connec- Fig. 8 is a side elevation of the same; tion with camera lenses. Fig. 9 is a front elevation of an annular re- 10 Mechanism of this kind as hitherto constructtaing plate for both the balanced key and the ro- 10 ed has generally comprised a fixed member with tatable member; an exterior thread, a rotatable member threaded Fig. 10 is a side elevation of the same; internally to engage said exterior thread so that Fig. 11 is a front elevation of a slidable memthe member, while rotating, has some translaber; and

tion along its axis, and the sliding member, Fig. 12 is aside elevation of the same. 15 adapted to slide on a cylindrical and key-wayed In the drawings, A is the fixed member adaptpo'rtion of the fixed member, has been provided ed to be fixed to a camera by means of the screw with a feather to engage the key-way and prethread a. B is the rotatable member mounted vent rotation, and the rotatable member has rotatably on the fixed me ber A. bein C011- been connected to the sliding member by a costrained thereon by their co-acting cylindrical 20 acting pair of screw threads of pitch different surfaces b and the shoulder b1 against which the from that of the aforesaid thread on the fixed end of the rotatable member B is held by elasmember. tic pressure means comprising the annular re- Such a ec anism has the defect that, as the taining plate C which is secured to the fixed direction of rotation of the rotatable member is member by two screws at 0 01. The annular 25 reversed, the sliding member is moved somewhat retaining P te C y be b to t -8 a Spring to one side of its true position, and this arises against a shoulder in of the rotatable member because of the eccentricity of the key and its B, bu I Prefer to p ace between the P e d unbalanced action whose effect is t m ve the said shoulder a cork ring D under elastic comsliding member from one side to the other of its D 88 this Serves both 85 a Spring to Press 30 normal concentric position, It turns, a far a the rotatable member against the shoulder In any slight looseness of fit permits, about the key and to provide desirable friction between the roas a fixed centre and not about the commo i tatable member and the fixed member. On the of symmetry. It has also the defect that th member B, and fixed preferably by screwing duty of preserving th axis of th hdab them together permanently by the threads 11;, 35 ber without lateral displacement r tilt i h m is an internal threaded portion In, its internal both by the cylindrical fitting between the s11d thread be being accurately concentric with the able and fixed members and by th r w d ntaxis of rotation of the member B. This I shall tings of the rotatable member, and these interhereafter refer to as the common axis. The ob- {erg with one another unless the fittings are ject Of attaching the portion In 130 the member 40 free, in which case backlash is inevitabl a d B instead of making them integral with one anlateral looseness probable. other is mainly a matter of convenience in as- The object of th present invenflpnisto'remedy sembly. Threaded within the screw b: is the these d fe t by improved design f th parts of slidable member E whose exterior threaded porth h i t pr vid h t 1 t a tion e is preferably so made that it bears in the 45 anced key, improved xi l st int of th co-acting screw thread b5 at three substantatable member and of the sliding member, and tially equidistant points, and this I prefer to seto effect other improvements, cure by removing the whole of the thread e be- I will describe my invention by reference to the we the Points 61 and 62 a ely 110 accompanying drawings, in which:-- to 120 degre s p r y li ing the member 1011- 50 Fig. 1 is a rear elevation of a complete screw zi inally at and along a circular arc e4 so mechanism according to the invention; that a tongue e5 is formed. Its free end es is Fig. 2 is a side elevation, the upper part in axial permanently set outwards and the tongue acts section, of the same; as a spring whereby the member is constrained Fig. 3 is an axial section of a fixed member within the rotatable member under elastic pressure substantially equal at the three points e1,

ex, ea. To prevent; rotation of the slidable member E as the rotatable member B is rotated, the fixed member A is provided with two inwardly projecting lugs a1 a: which act as feathers. Their sides are in parallel planes parallel to the common axis, and the lugs are preferably diametrically opposite to one another or approximately so. Fitting slidably on the parallel sides of the lugs a1 a: is an annular balanced key F notched in its peripheral edge at I ii to fit the lugs a1 a: aforesaid, but the notches are suficiently deep and the peripheral edge of the balanced key has sufiicient. freedom in the fixed member A to permit the key to slide radially in the member A, although withoutrotation, to an extent sufficlent to cover the aggregate errors of concentricity of the various members. 'I'he balanced key F has, in turn, two inwardly projecting lugs la f4 with parallel sides in planes parallel to one another, normal to the surface of the balanced key, intermediate between the notches f1 f2, and preferably in oneplane therewith and not displaced relative to the others along the common axis. The lugs fa ii in the balanced key 1? con stitute feathers which engage longitudinal slots e1 2;, in the tubular hub es of the slidable member E. The peripheral surface em of the slidable member E is smaller than the bore ft of the balanced key P so that it has freedom to move radially in the balanced key and retaining plate as aforesaid, to cover the aggregate errors of concentricity of the various members.

Means are desirable to constrain the key in a position normal to the common axis, and this may be accomplished, when space. permits, merely by making the balanced key and. the feathers of suflicient thickness longitudinally; but, as in the case illustrated, where space is restricted, we may constrain the ring as by placing it between a shoulder as i'ormed'in therecess (u in the fixed member A and the annular retaining plate C, but so that it is free to float radially. Means such as the arcuate slot be in the face of the rotatable member B and the pin as, fixed in the member A and adapted to abut against the ends of said arcuate slot, are provided to prevent overturning of the rotatable member B.

I am aware that numerous changes in construction can be made without departing from the principles. of my invention and I do not desire to limit the scope of my claims except as required by the prior art.

What is claimed is:

1. In a precision screw mechanism, 'the combination of a fixed member, a rotatable member rotatable thereon and screw threaded concentrically to the axis of such rotation, a slidable member adapted to engage the thread in the rotatable member and to be moved longitudinally by the rotation thereof, and a balanced key engaging the slidable member and the fixed member to constrain the slidable member against rotation.

2. In a precision screw mechanism, the combination of a. fixed member, a rotatable member rotatable thereon and screw threaded concentrically to the axis of such rotation, a slidable member adapted to engage the thread in the rotatable member and supported wholly by the rotatable member and to be moved longitudinally by the rotation thereof, and a balanced key engaging the slidable member and the fixed member to constrain the slidable member against rotation.

3. In a precision screw mechanism, the combination of a fixed member, a slidable member, and a balanced key adapted to constrain the slidable member against rotation relative to the fixed member, a rotatable member, a screw thread thereon adapted to co-operate with a thread on the slidable member, the rotatable member being constrained for rotation without longitudinal movement on the fixed member by means including co-acting cylindrical surfaces on the rotatable member and the fixed member, a shoulder on one and a co-acting bearing surface on the other, and elastic pressure means for holding the shoulder and the surface in co-operative relation.

4. A precision screw mechanism comprising in combination a fixed member, a rotatable member adapted for rotation on the fixed member, a slidable member carried wholly by said-rotatable member V-screw threaded to co-operate with a screw thread in the rotatable member and so formed that it bears in the rotatable member at three points approximately at equal angular separation, elastic pressure means by which the slidable member at one of said points is urged radially toward the rotatable member so as to remove all shake between the two members, and a balanced key to constrain the slidable member against rotation on the fixed member.

5. In a precision screw mechanism, the combination of a fixed member, a slidable member, and a balanced key adapted to constrain the slidable member against rotation relative to the fixed member, a rotatable member, a screw thread thereon adapted to co-operate with a thread on the slidable member, the rotatable member being constrained for rotation without longitudinal movement on the fixed member by means including co-operating elements on the rotatable and fixed members so formed as to constrain the rotatable member to rotate on the fixed member on a fixed axis, and elastic pressure means for holding the elements together.

WILLIAM TAYLOR. 

